a) Field of the Invention
This invention relates to a process for producing indene from an indene-containing coal tar distillate, and more specifically to a process for producing high-purity indene by adding a glycol or a derivative thereof (hereinafter simply called xe2x80x9ca glycolxe2x80x9d) to an indene-containing coal tar distillate and then conducting azeotropic distillation to have practically indene alone distilled selectively while allowing benzonitrile to concentrate in a bottoms residual or by adding a glycol or a particular extractant and then conducting extractive distillation to have practically indene alone distilled selectively while allowing benzonitrile to concentrate in a bottoms residual.
b) Description of the Related Art
An indene-containing distillate available from distillation of a coal tar distillate contains components hardly separable from indene by distillation. Additional purification procedures are needed to purify indene further. Impurities in such an indene distillate include inter alia benzonitrile, indane, alkylbenzenes, oxygen-containing organic compounds such as phenols, and nitrogen-containing organic compounds such as pyridines and anilines. It is known that among these, phenols, pyridines and anilines can be eliminated by treatment with an aqueous alkali or acid solution. Further, indane can be eliminated by precision distillation. Benzonitrile and alkylbenzenes, however, cannot be eliminated even when treated with an aqueous acid or alkali solution. Even if precision distillation is conducted, they cannot be separated satisfactorily.
Known conventional processes for the elimination of benzonitrile from an indene distillate include: a process for eliminating benzonitrile as a benzoate salt by hydrolyzing benzonitrile under heat in an aqueous alkali solution (JP 09-301898 A); a process for azeotropically eliminating benzonitrile by adding furfural or n-hexanol; a process making use of adsorptive separation; a crystallization process; and a process for azeotropically distilling benzonitrile by adding a phenol, an alcohol, an amine or the like (U.S. Pat. No. 2,279,780, JP 60-87230 A).
However, the process which features hydrolysis of benzonitrile requires use of an aqueous alkali hydroxide solution of high concentration and treatment for long time at high temperature. Moreover, the resulting benzoate leads to formation of an aqueous emulsion, handling of which is difficult. The process making use of adsorptive separation is not suited for the treatment of a great deal of feed. The process which relies upon crystallization is extremely difficult for actual practice from the standpoint of industrial scale, treatment of a great deal of feed (indene-containing coal tar distillate) and cost.
Further, the azeotropic distillation process disclosed in U.S. Pat. No. 2,279,780 azeotropically eliminates light components other than indene by incorporating a compound, which contains one or more polar groups such as hydroxyl groups, carboxyl groups or amino groups, as an additive in a coal tar distillate and then conducting precision distillation. According to this process, the components having lower boiling points than indene are firstly eliminated together with the polar additive from the top of a distillation column in an initial stage of the distillation, and subsequent to distillation of indene and the additive, components heavier than indene are obtained as a bottoms residual. This process is, however, not fully effective from the viewpoint of elimination of benzonitrile. Moreover, the additive is contained in the respective distillate fractions and the bottoms residual, and in view of the need for recycled use of the additive, this process is not considered to be readily usable in practice.
According to the process disclosed in JP 60-87230 A, on the other hand, a phenol is added to a coal tar distillate, and indene and the phenol are then azeotropically distilled while allowing components heavier than indene, such as benzonitrile, to obtain as a bottoms residual. In this process, the concentration of indene in the azeotropic distillate is certainly higher than that of indene in the coal tar distillate before the azeotropic distillation. Nonetheless, the azeotropic distillate contains the phenol at a considerably high concentration. For the production of high-purity indene, addition of the phenol in a large amount as an entrainer is indispensable although the phenol can be extracted in an aqueous alkali solution. Accordingly, to treat the phenol in the distillate recovered by the distillation, the treatment with the aqueous alkali solution results in a substantial load. Moreover, post treatment of the waste alkali leads to a further problem.
No satisfactory process is, therefore, considered to have been established yet for the elimination of benzonitrile from indene.
Therefore, an object of the present invention is to overcome the above-described problems of the conventional art and hence, to provide a process for the production of indene, which makes it possible to easily obtain high-purity indene.
The above-described object can be achieved by the present invention to be described hereinafter.
In a first aspect of the present invention, there is thus provided a process for producing indene, which comprises adding a glycol or a derivative thereof to an indene-containing coal tar distillate, and then conducting azeotropic distillation to obtain an indene fraction while eliminating benzonitrile from the indene-containing coal tar distillate.
In a second aspect of the present invention, there is also provided a process for producing indene, which comprises adding a glycol or a derivative thereof to an indene-containing coal tar distillate, and then conducting extractive distillation to obtain an indene fraction while eliminating benzonitrile from the indene-containing coal tar distillate.
In a third aspect of the present invention, there is also provided a process for producing indene, which comprises adding to an indene-containing coal tar distillate an extractant selected from the group consisting of dialkyl carbonates, alkylene carbonates and diaryl carbonates, and then conducting extractive distillation to obtain an indene fraction while eliminating benzonitrile from the indene-containing coal tar distillate.
According to the first aspect of the present invention, the azeotropic distillation of the indene-containing coal tar distillate in the presence of the glycol can effectively change the volatility of benzonitrile, that is, can form an azeotrope of the glycol and indene, whereby practically indene alone can be selectively distilled to obtain high-purity indene. When ethylene glycol is used as an illustrative glycol here, an azeotrope is formed with indene and ethylene glycol so that indene is recovered as a low boiling-point fraction while benzonitrile is allowed to concentrate as a high boiling-point fraction in a bottoms residual.
According to the second or third aspect of the present invention, on the other hand, the extractive distillation of the indene-containing coal tar distillate in the presence of the glycol or extractant can effectively change the volatility of benzonitrile, that is, can effectively extract benzonitrile owing to the addition of the glycol or extractant, whereby practically indene alone can be distilled to obtain high-purity indene. When triethylene glycol is used as an illustrative glycol or ethylene carbonate is employed as an illustrative extractant, practically indene alone is distilled, and components heavier than indene are recovered together with triethylene glycol or ethylene carbonate as a bottoms residual.